Online Encyclopedia


Online Encyclopedia
Originally appearing in Volume V19, Page 55 of the 1911 Encyclopedia Britannica.
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MUSCULAR SYSTEM from the posterior primary divisions of the spinal nerves (see NERVE, SPINAL). On the anterior part of the thoracic region the pectoralis major runs from the clavicle, sternum and ribs, to the humerus (fig. 6) ; deep to this is the pectoralis minor, passing from the upper ribs to From A. M. Paterson, Cunningham's Text Book of Anatomy. process of the atlas. These muscles move the head on the atlas forming the semispinalis and multifidus spine muscles. The and the atlas on the axis. They are supplied by the posterior branch latissimus dorsi and rhomboids are supplied by branches of the of the first cervical nerve. brachial plexus of nerves, while the deeper muscles get their nerves MUSCLES OF THE TRUNK.—The trapezius has already been de- scribed as a superficial muscle of the upper part of the back; in the loin region the latissimus dorsi (fig. 5) is the superficial muscle, its origin being from the lower thoracic .spines, lower ribs and lumbar fascia, and it is inserted into the upper part of the arm bone or humerus. When the trapezius is cut, the rhomboid muscles (major and minor) passing from the upper thoracic spines to the vertebral border of the scapula are seen, and deep to these is the serratus posticus superior passing from nearly the same spines to the upper ribs. On reflecting the latissimus dorsi the serratus posticus inferior is seen running from the lower thoracic spines to the lower ribs. When these muscles are removed the great mass of the erector spinae is exposed, familiar to every one as the upper cut of the sirloin or ribs of beef ; it runs all the way up the dorsal side of the vertebral column from the pelvis to the occiput, the complexus already mentioned being its extension to the head. It i3 longitudinally segmented into many different bundles to which special names are given, and it is attached to the various vertebrae and ribs as it goes up, thus straightening the spinal column. Deep to the erector spinae are found shorter bundles passing from one vertebra to another and the coracoid process. The serratus ma gnus is a large muscle rising by serrations from the upper eight ribs, and running back to the vertebral border of the scapula, which it draws forward as in the fencer's lunge. Between the ribs are the external and internal inter-costal muscles; the former beginning at the tubercle and ending at the junctions of the ribs with their cartilages, while the latter only begin at the angle of the ribs but are prolonged on to the sternum, so that an interchondral as well as an intercostal part of each muscle is recognized. The fibres of the external intercostals run downward and forward, those of the internal downward and backward (see RESPIRATION). The abdominal walls are formed of three sheets of muscle, of which the most superficial or external oblique (fig. 6) is attached to the outer surfaces of the lower ribs; its fibres run downward and forward to the pelvis and mid-line of the abdomen, the middle one or internal oblique is on the same plane as the ribs, and its fibres run downward and backward, while the transversaiis is attached to the deep surfaces of the ribs, and its fibres run horizon-tally forward. Below, all these muscles are attached to the crest of the ilium and to Poupart's ligament, which is really the lower free edge of the external oblique, while, behind, the two deeper ones, at all events, blend with the fascia lumborum. As they approach the mid-ventral line they become aponeurotic and form the sheath of the rectus. The rectus abdominis (fig. 6) is a flat muscular hand which runs up on each side of the linea alba or mid-ventral line of the abdomen from the pubis to the ribs and sternum. This muscle has certain tendinous intersections or lineae transversae, the positions rotating muscles pass from the scapula to the upper end of the humerus; these are the subscapuloris passing in front of the shoulder joint, the supraspinatus above the joint, and the infraspinatus and teres minor behind. The teres major (fig. 5) comes from near the lower angle of the scapula, and is inserted with the latissimus dorsi into the front of the. surgical neck of the humerus. The coracobrachialis (fig. 7) passes from the coracoid process to the middle of the humerus in front of the shoulder joint, while the brachialis anticus passes in front of the elbow from the humerus to the coronoid process of the ulna. Passing in front of both shoulder and elbow is Coracoid process PECIORALIS
End of Article: MUSCULAR

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